How to start a background service using Package.appxmanifest?

public class PushNotificationBackgroundService : IBackgroundTask
{
    // Entry point that should eventually be called
    public async void Run(IBackgroundTaskInstance taskInstance) {...}
}

<Applications>
    <Application Id="App"
                 Executable="$targetnametoken$.exe"
                 EntryPoint="$targetentrypoint$">
        <Extensions>
            <Extension Category="windows.backgroundTasks" EntryPoint="$targetentrypoint$.PushNotificationBackgroundService">
                <BackgroundTasks>
                    <Task Type="pushNotification"/>
                </BackgroundTasks>
            </Extension>
        </Extensions>
    </Application>
</Applications>